Effect of Pre-/Post-Heat Treatment on Pasteurization of Bacillus subtilis Spore Suspended in Soy Milk by Medium High Hydrostatic Pressure Treatment

Medium high hydrostatic pressure (MHHP) treatment can induce the spore to germinate via activating germination receptor and subsequently to lose heat tolerance of the spore and finally to kill the germinated spore although the ungerminated spore even after MHHP treatment can be survived. This study aims to clarify effect of post-/pre-heat treatment on pasteurization of Bacillus subtilis spore suspended in soy milk as a food model by MHHP treatment. In the result, D value, as known heat tolerance indicator, of the MHHP treated spore was decreased in comparison with the untreated spore. However, activation energy required for killing both of the untreated and the MHHP-treated spore were equivalent, which indicated that MHHP treatment might increase heat conductivity of the ungerminated spore after MHHP treatment. When the spore was subjected to pre-heat treatment and subsequently to MHHP treatment, pasteurization effect of MHHP treatment was differed to the heating temperature. Pre-heat treatment at 80 C promote the pasteurization while that at 90-100 C, which might be caused by heat activation/inactivation of germination receptors. From these results, combination of MHHP treatment with post-/pre-heat treatment could be effective for pasteurization of B. subtilis although pre-heat treatment was limited lower temperature than 80 C.